Fluidic operators are normally provided for the operation of fail-safe valves in well head assemblies. Since it is necessary to quickly close such valves upon command or when a particular well head condition is sensed, generally pneumatic operators are provided for the valves, the air in the operator cylinder being exhausted directly into the atmosphere upon closing of the fail-safe valve. This exahaustion of air into the atmosphere provides a rapid closing time due to a minimum back pressure and not having to recycle the air. Under many circumstances, however, hydraulic actuators are more desirable than pneumatic actuators. Additionally, it is sometimes desirable to effect actuation of the operators with a gaseous fluid that is noxious (i.e., H.sub.2 S), and should not be vented to atmosphere. Under such circumstances, upon closing of the fail-safe valve, the fluid must be returned to the fluid reservoir.
In the case of the use of hydraulic fluid for actuation, the necessity for recycle of the hydraulic fluid results in longer closing time or larger lines or both, often times making hydraulic actuation infeasible. There have been proposals for the rapid closing of valves with hydraulic actuators, such as shown in U.S. Pat. No. 3,495,501, however such proposals do not necessarily result in the desired closing quickness, and often require a large number of complicated arrangements including two sources of high pressure hydraulic fluid, a check valve and three other valves, each valve being a three-way or more valve, etc.
According to the present invention, an actuator is provided, especially suited for rapid closing of a fail-safe valve, which is relatively simple yet provides for rapid valve closing and recycle of the actuating fluid. [While the invention will be described with particular reference to hydraulic fluid, it is to be noted that other fluids besides hydraulic fluids may be utilized, and the invention is not to be limited to hydraulic fluids.] According to the present invention, a piston actuator is provided disposed in the cylinder and dividing the cylinder into first and second chambers, the piston movable in a first direction to shrink the first chamber and effect rapid valve closing, and movable in a second direction to shrink the second chamber for opening with the valve. Biasing means are disposed in the second chamber for biasing the piston operator for rapid closing, and the first and second chambers are constructed so that the maximum displaceable volume of the first cylinder chamber is equal to or less than the maximum displaceable volume of the second cylinder chamber. During closing of the valve, the fluid displaced from the first piston chamber is vented to the second piston chamber rather than being pumped back the distance to the hydraulic reservoir, so that the minimum resistance to piston movement is provided. During the application of high pressure hydraulic fluid to the first chamber to open the valve, the fluid in the second chamber is then ultimately pumped back to the reservoir.
An integral valve assembly is provided for valving fluid to the first and second chambers from and to a high pressure source of hydraulic fluid and a hydraulic reservoir. The integral valve assembly includes a first passageway in the block leading from a first opening to the exterior of the block to a second opening to the exterior, a first check valve disposed in the first passageway for allowing passage of fluid from the first opening to the second opening but not vice-versa, a second passageway in the block leading from a third opening to the exterior of the block to the first check valve operator to bias the operator closed to prevent passage of fluid through the first passageway past the check valve in either direction, a third passageway in the block leading from the third opening to the second opening, a second check valve disposed in the third passageway for allowing passage of fluid from the third opening to the second opening but not vice-versa, and a fourth passageway in the block leading from the second opening to a fourth opening to the exterior of the block. A plurality of valve assemblies may be stacked one upon the other for providing operation of a plurality of fail-safe valves, common fluid supply and fluid drain lines being provided for the assemblies. According to the invention, only two simple check valves need be provided for effecting the valving operations for rapid closing of a fail-safe valve and for opening thereof.
It is the primary object of the present invention to provide hydraulic operator means capable of rapid movement in one direction, utilizing a minimum number of simple components. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.